Mass spectrometry

ABSTRACT

A mass spectrometer in which plural beams of ions are generated from a common substance for simultaneous passage through an analyzer region. An auxiliary electrostatic analysis is performed on one of the analyzed beams which are received by separate collectors. Metastable ions are observed at one collector while their parents are observed at another collector.

nited States Patent 1 Merren Mar. 12, 1974 MASS SPECTROMETRY 3,649,8273/1972 Bell 250/419 ME 7 I t T l 1 Hale FOREIGN PATENTS OR APPLICATIONS1,134,448 11/1968 Great Britain 250/41.9 ME [73] Ass1gnee: AssociatedElectrIcal Industries Limited, London, England Filed: Dec. 13,1971Przmary Exammer-Walter Stolwem Assistant Examiner-C. E. Church ForeignApplication Priority Data [57] ABSTRACT Dec. 18, 1970 Great Britain60229/70 A mass spectrometer in which plural beams of ions are generatedfrom a common substance for simultaneous [52] US. Cl 250/285, 250/285,250/296 passage through an analyzer region An auxiliary elec [51] Int.Cl. H01 39/34, BOld 59/44 trostatic analysis is performed on one of theanalyzed [58] Field Of Search ME, G beams are received y Separatecollectors. Metastable ions are observed at one collector while [56]References C'ted their parents are observed at another collector.

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A TTORNEYS MASS SPECTROMETRY CROSS REFERENCE TO RELATED APPLICATIONS ANDPATENTS Plural Beam Mass Spectrometer," Ser. No. 73,072, filed Sept. 17,1970, by Brian Green.

Plural Beam Mass Spectrometer for Conducting High and Low ResolutionStudies, US. Pat. No. 3,573,453, filed May 12, 1967 by Patrick Powers.

Beam Correcting Device for Mass Spectrometers and Method of Operation,Ser. No. 39,240, filed May 15, 1970 by Sidney Evans and Reginald Graham.

BACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relates to mass spectrometers and more particularly to aplural beam mass spectrometer in which a plurality of beams can begenerated simultaneously and passed concurrently through a commonanalyzer region.

2. Prior Art In the analysis of substances with a mass spectrometer,ions of a substance being analyzed are generated in an ion source andthen emitted from the source as an ion beam. The beam passes through, inthe case of a single-focusing mass spectrometer, a magnetic analyzer;and in the case of a double-focusing mass spectrometer, an electrostaticanalyzer and then a magnetic analyzer.

During a given analytical study, the accelerating voltage of the sourceor the voltage applied to the magnetic analyzer may be varied to scanthe instrument. As the instrument is scanned, ions of differentmass/charge ratios are deflected onto the collectors successively andthe sample is thus analyzed.

In the referenced Powers patent, there is a disclosure of, among otherthings, the use of two ion sources which are capable of simultaneouslyproducing two ion beams. The two beams are passed, in a common ion tube,through a single analyzer system and then collected respectively on eachof two collectors. The two beams may be passed through the ion tubeeither simultaneously, or selectively, one at a time.

SUMMARY OF THE PRESENT INVENTION With the present invention one or moresources are positioned for emitting plural ion beams simultaneously.Each emitted beam passes through in the preferred embodiment,electrostatic and magnetic analyzers of relatively conventionalconstruction. With the present invention there is provision of adivergentdeflector which may be referred toas the analyzed beamdeflector. The divergent deflector deflects one of the beams away fromthe other after their passage through the analyzers.

The divergent deflector is an electrostatic deflector. Since it is anelectrostatic deflector, it functions in a manner comparable to theelectrostatic analyzer. This means that, ions undergoing metastabletransitions in the analyzer are not deflected to the collector, butrather only parent ions, or fragments produced in the source, or thoseions very close to the mass/charge ratios of the parent ions reach thecollector; Thus, a metastable study may be conducted witha beam which isnot deflected after it transverses the collector slit, while the parentions in the other beam are analyzed.

Other objects and a fuller understanding of the invention may be had byreferring to the following description and claims taken in conjunctionwith the accompanying, drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. l is a schematic view of a massspectrometer partially in section in a plane of deflection of theanalyzers of a preferred embodiment;

FIG. 2 is a fragmentary, partially schematic, plan view of a massspectrometer showing the deflectors of the preferred embodiment;

FIG. 3 is an electrical schematic drawing showing the deflectors of thepreferred embodiment and the circuitry for supplying power to them;

FIG. 4 is a plan view of the converging deflectors of the preferredembodiment; and,

FIG. 5 is a plan view of the auxiliary electrostatic analyzer of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings and toFIG. l in particular, ion sources are in a source section showngenerally at 110. The sources generate plural ion beams which areaccelerated by electrodes within the sources through exit slitsindicated schematically at 1111. After the beams have passed through theexit slits Ill, they pass through a source convergent deflector section13 which will be described in greater detail presently. The convergentdeflector brings the beams relatively close together. The beams thenpass through an electrostatic analyzer 14 of relatively conventionalconstruction.

After a beam has passed through the electrostatic analyzer 14, it maypass through an ion current collector or monitor 15. Ion collectors areknown in the art and the collector 15 may be of known and conventionalconstruction other than for modification to accommodate plural beams.The beam next passes through a magnetic analyzer 16 where it is furtherdeflected. After the beam passes through the magnetic analyzer 16, itpasses through a collector slit structure shown schematically at 117.

After the beams have passed through the slit structure 17, they passthrough an auxiliary electrostatic analyzer section 18. Where there aretwo beams in the preferred construction, one beam passes through thedivergent deflection section without further deflection and the other isdeflected. After traversing the divergent deflection section, the beamsenter a collector section 19. In the disclosed embodiment, one collectorin the form of an electron multiplier tube 20 is shown in FIG. 11.

Referring now to FIG. 2, a somewhat diagrammatic plan view of atwo-source double-beam mass spectrometer is shown. The source section 10is composed of a pair of ion sources in source housing 25, 26. Thesource housings 25, 26 define separated chambers 27, 28 respectively.The separated chambers 27, 28 are respectively and individually pumpedthrough exhaust passages 29, 30 to maintain conventional vacuumconditions in the source chambers 27, 28.

Within each source chamber 27, 28 an ion generating source ofconventional construction is positioned. Each source may be, forexample, a conventional electron bombardment source. On the other hand,one of the features of a plural beam mass spectrometer is that thesources need not be identical. One may provide two types of sources suchas electron bombardment and field ionization to provide greaterflexibility in conducting studies.

As is clearly indicated by the schematic showing of FIG. 2, ion beamsindicated by pairs of dashed lines 32, 33 are emitted from the sources.These beams, as emitted through the exit structure 11, are relativelywidely spaced. If a study were conducted with the beams so spaced, itwill be appreciated that very large electrostatic and magnetic analyzers14, 16 would be required and particularly the magnetic analyzer would beof large mass and expensive.

One of the optional features of this invention is pro vided in thesource convergent deflection section 13. In this section, each of thetwo beams 32, 33 is first deflected to a convergent path so that thebeams approach one another and thereafter are deflected in the oppositedirection to bring the beams back into parallel, but now much moreclosely spaced, relationship.

The convergent deflecting section is positioned within an evacuated massspectrometer housing 35. The housing 35 thus envelopes not only, as isknown in the art, the electrostatic and magnetic analyzers andcollectors but also the convergent and divergent deflector sections.

The convergent deflector section has two pairs of oppositely chargedconvergent sectors or deflector plates 36, 37 and 38, 39. The convergentsectors 36, 37 de flect the beam 32 toward the beam 33; and, conversely,the sectors 38, 39, deflect the beam 33 toward the beam 32. It will beseen that faces 36A-39A of the sectors of each pair are arcuatelycurved, defining segments of cylinders of common curvature. Thecurvature of these faces is equivalent to the curvature of the beams 32,33 as thev pass through their respective and associated convergentsectors.

The beams next pass through spaces delineated by a central common sector40 and parallel path-producing sectors 41, 42, respectively. The sectors41, 42 are charged so that the beams are oppositely deflected, throughan angle corresponding to the angle produced in the convergent sectors,to bring the beams back into parallel but closer relationship.

The sectors 40-42 also have arcuately curved faces that are segments ofcylinders. Thus, the common segment has a face 40A which is concentricto a face 41A and a face 408 which is concentric to a face 42A. Thesefaces have curvatures corresponding to the desired curvature of the beamin the plane of FIG. 2 and equal and opposite to the curvature of theconvergent sectors.

In mass spectrometry, since the molecules from which the ions are formedhave random thermal velocity in the ion source, ions commonly have asmall component of velocity in a direction that is in the plane of thedrawing of FIG. 2. Therefore, to prevent any intermixing of the beams32, 33, a collimating slit structure 45 is provided. Collimating slitstructure 45 respectively has collimating slit apertures 46, 47 for thebeams 32, 33.

The deflected and collimated beams 32, 33 traverse through a common iontube, a portion of which is shown at 50. While in the tube, they passthrough the electrostatic and magnetic analyzers 14, 16 and thencethrough the collector slit structure 17. As has been indicatedpreviously, the magnetic analyzer causes ion beam curvature.Accordingly, the slit structure 17 has slit openings 51, 52 which arecanted with respect to the plane of analyzer deflection, i.e., the planeof FIG. 1, and are in non-parallel relationship with one another. Afterthe beam 32 has passed through the slit 5], it proceeds, without furtherdeflection, to the electron multiplier 20. Since the beams are too closetogether to permit another electron multiplier 53 to be positioned inthe path of the beam 33, the beam 33 is deflected outwardly in theauxiliary electrostatic analyzer section 18.

The auxiliary electrostatic analyzer section 18 performs an auxiliaryelectrostatic analysis on the beam 33, after it has been analyzed by theanalyzers 14, 16 in common with the beam 32. The auxiliary analyzer iscomposed of electrically charged sectors 54, 55. These sectors, like thesectors in the convergence region 13, have arcuately curved surfaces54A, 55A each of which defines a segment of a cylinder. The curvature ofthe surface 54A, 55A is, again, a curvature corresponding to the desiredbeam deflection curvature.

It will be appreciated that both beams can be analyzed, but forsimplicity of manufacture and to facilitate the metastable studiesdescribed above, auxiliary analysis of only one of the two beams ispreferred.

The instrument is constructed such that the total lengths of the path oftravel of the two beams 32, 33 are identical from their respectivesources to their respective collectors. This permits precise comparativeanalysis of the two beams which have been analyzed in identicalconditions.

In FIG. 3, a suitable method of deriving appropriate voltages for thevarious deflection sectors is shown. An array of fixed and variableresistors Rl-Rl4 is connected across an accelerated beam voltage supply60. Suitable voltages are tapped from the array of resistors to giveappropriate relative potentials between the ion sources 25, 26 and thesectors of the regions 13, 18.

The resistors R1 and R2 are preferably such that a major portion of thevoltage from the accelerating voltage supply appears across R1, forexample a positive voltage of 4,000 volts, and a minor portion appearsacross resistor R2, for example a negative voltage of 200 volts. Thepotentials for the sectors of the deflection regions are preferablyarranged to be substantially equal and positive and negative withrespect to ground. Suitable potentials for the sectors of the convergentregions 13 are plus and minus 170 volts and for the sectors of thedivergent deflector plus and minus 60 volts. The potentials of at leastone sector of each pair are preferably adjustable as shown in FIG. 3 bymeans of variable resistors R6, R7, R12, R13, R14. Apart from enablingthe metastable analysis of the invention, the

variable resistors allow for setting up the mass spectrometer foroperation and compensate for any errors in the manufacture of aspectrometer.

While FIGS. 2 and 3 are schematically illustrative of the arrangementand operation of the deflectors of the present invention, theconstruction of the deflectors is shown in more detail in FIGS. 4 and 5.At the outset it should be noted that FIGS. 4 and 5 are mirror reversalsof the arrangements shown in FIGS. 2 and 3. Hence the ion beams travelright to left in FIGS. 4 and 5 rather than left to right as in FIGS. 2and 3.

Referring to FIG. 4, the convergent deflector section 13 has annularmounting plates 100. A pair of housings 101, 102 are secured to themounting plate and are aligned by means of dowel pins 103. The housings101, 102 have cup-shaped tubular side wall portions 104, 105respectively defining upper and lower cylindrical chambers 106, 107. Thehousings also have mounting flanges 108, 109 which receive the dowelpins 103 and which connect with an inwardly extending annular flange 110of the spectrometer housing 35. By this arrangement, the mounting plate100 and the housings 101, 102 are supported within the vacuum evacuatedenvironment of the mass spectrometer housing 35.

A pair of elongate supports 111, 112 extend respectively into thehousings 101, 102. The elongate supports 111, 112 are each ofsubstantially semi-circular cross-section, having end wall portions ofincreased thickness to receive threaded fasteners 113, 114. Thefasteners 113 extend through the mounting plate 100 to secure thesupports 11], 112 in place. The fasteners 114 mount end plates 115, 116on the supports 111, 112.

The convergent deflectors 36, 37 and 38, 39 are spaced from the endplates 115, 116 by glass balls 117. Threaded fasteners 118 ofelectrically insulative material extend through openings in the endplates 115, 116 and into threaded apertures in the deflectors 36, 39.The deflectors 36, 39 are thus carried by and insulated from the endplates 115, 116. A pair of fringe field correction plates 119, 120 arespaced from the opposite ends of the deflectors36, 37 and 38, 39 byglass balls 121. Electrically insulated threaded fasteners 122 extendthrough openings in the plates 119, 120 and into threaded apertures inthe deflectors 36, 39 to support the plates 119, 120 from thedeflectors. A pair of cross deflection plates 123, 124 and a pair ofshield assemblies designated generally by the numerals 125, 126 may alsobe supported from the fasteners 122. The shield assemblies 125, 126respectively include shields 127, 128 which are maintained at groundpotential and which are positioned parallel to the beams 32, 33 withinthe region intermediate the deflectors 36, 37, 38, 39 and 40, 41, 42.

A tubular support 130 extends leftwardly of the mounting plate 100. Thetubular support has ends of enlarged thickness to receive threadedfasteners 131, 132. The fasteners 131 extend through the mounting plate100 and secure the support 130 in place. The fasteners 132 mount a plate133 from the tubular support 130.

The plate 133 has openings 134 formed therethrough. An annular plate 135is positioned to the left of the plate 133 and is spaced in parallelrelationship therefrom by glass balls 137. Threaded fasteners 138 extendthrough openings in the plates 135, 136 and through the openings 134 andinto threaded apertures in the deflector sectors 41, 42. The deflectorsectors 41, 42 are spaced from the plate 133 by glass balls 139. Aclamping arrangement is thereby provided for supporting the sectors 41,42 from the plate 133, while the glass balls 137, 139 simultaneouslyserve to insulate the sectors 41, 42 from the plate 133. Moreover, theplate 135 is also seen to be insulated from the plate 133. A tube 140 issecured to the plate 135. The ion beams 32, 33 enter the analyzer region14 through the tube 140.

A pair of plates 141, 142 are spaced from deflector sectors 41, 42 byglass balls 143. Electrically insulated fasteners 144 extend throughopenings in the plates 14], 142 and into threaded apertures in thesectors 41,

42. The plates 141, 142 are thereby insulated from and carried by thesectors 41, 42. The plates 141, 142 may be maintained at groundpotential while the deflector sectors 41, 42 may be electrically chargedas previously explained. The central deflector sector 40 is supportedintermediate the sectors 41, 42 by fasteners, not shown.

It will be understood that the plates 115, 116, 119, 120 and 141,142,133 which are positioned adjacent the ends of the deflectors 36, 37,38, 39 and 40, 41, 42 respectively each have openings therethrough forthe passage of the ion beams, and serve as field correction plates tocorrect for the field end effects which are present adjacent thedeflector ends.

Referring to FIG. 6 the auxiliary analyzer section 18 is seen to includea main block 150. The main block connects with a tubular body 151. Thetubular body 151 has a centrally located opening 152 through which thebeams 32, 33 pass as they emerge from the region of the magneticanalyzer 16. From the tubular body 151, the beams 32,- 33 pass into achamber 153 formed within the main block 150. The beam 32 passes withoutfurther deflection to the electron multiplier 20. The beam 33 isdeflected downwardly to the electron multiplier 21 by means of theelectrically charged deflector sectors 54, 55, whereby an auxiliaryelectrostatic analysis is performed on the beam 33. The sectors 54, 55are supported inside the chamber 153 by fasteners, not shown.

The electron multipliers 20, 21 are of a construction well known in theart and need not be described in detail. The multipliers 20, 21 arepositioned within housings 154, 155 which are secured to the main block150 in such fashion as will assure the preservation of a vacuumenvironment within the chamber 153. A pair of amplifiers 156, 157amplify the signals from the multipliers 20, 21 in the usual fashion. Acover plate 158 is secured to the main block 150 so as to provide avacuum seal.

Two mass spectrometric methods are possible with the above describedapparatus. (In both methods, the ion beams are formed from the samesubstance or mixture of substances, in order that the metastableanalysis may be meaningful, but this does not preclude an additionalsubstance, such as a reference substance, being added to one ion sourceonly).

In the first method, the voltages applied to the sectors 54 and 55 are(by suitable adjustment of the variable resistors R8 and R12) such thatmetastable ions formed during and after passage of the ion beams 32 and33 through the main analyzers 14 and 16 are substantially excluded fromthe ion collector (53) in the path of ions passing through the auxiliaryelectrostatic analyzer formed by the sectors 54 and 55, and also suchthat ions which have been formed in the ion source 28 and which have notundergone subsequent transitions pass through the auxiliaryelectrostatic analyzer to the ion collector 53.

In the second method, the auxiliary electrostatic analyzer can be usedto investigate metastable ions fonned after the main analyzers 14 and16. The auxiliary analyzer is situated after the resolution slit.52 inthe path of the ion beam 32, and therefore any metastable ions formed inthe region between the main analyzers 14 and 16 and the auxiliaryelectrostatic analyser will be rejected if the potential between thesectors 54 and 55 is set (by means of R12) so that the parent ions arecollected by the collector 53 associated with the auxiliary analyzer.(This may be contrasted with a single beam mass spectrometer in which anion which passes through the exit face of the main analyzers and throughthe resolution slit is collected by the ion collector even if itdissociates and forms a metastable ion in this part of its path.)

The voltage between the sectors 54 and 55 may be scanned so that thespectrum of the metastable ions formed in the region between themagnetic analyzer l6 and the auxiliary electrostatic analyzer can beobtained. Scanning can be undertaken by suitable manual variation of theresistor R12 or alternatively by connecting the sectors 53 and 54 to asuitable source of scanning voltage.

Although the invention has been described in its preferred form with acertain degree of particularity, it is understood that the presentdisclosure of the preferred form has been made only by way of exampleand that numerous changes in the details of construction and thecombination and arrangement of parts may be resorted to withoutdeparting from the spirit and the scope of the invention as hereinafterclaimed.

What is claimed is:

1. A method of mass spectrometry performed with a plural beam massspectrometer wherein a plurality of ion beams formed from a commonsubstance are passed through a common analyser means including magneticand electrostatic analysers and collected by individual ion collectors,comprising the steps of further electrostatically analysing one of thebeams between the common analyser means and the respective ioncollector, and directly collecting at least one other ion beam on arespective other ion collector without electrostatic analysis of saidother ion beam between the common analyser means and said other ioncollector.

2. The method of claim 1, wherein metastable ions are collected by saidrespective ion collector and parent ions of said metastable ions arecollected by said other ion collector.

3. The method of claim 1, wherein parent ions are collected by saidrespective ion collector and metastable ions are collected by said otherion collector.

4. The method of claim 1 wherein the further electrostatic analysis ofsaid one of the beams is performed by making a scanning variation of anelectrostatic field.

5. The method of claim 1 wherein the further electrostatic analysis ofsaid one of the beams is performed with a fixed electric field.

6. A method of mass spectrometry performed with a double-beam massspectrometer having ion source means, a common analyser means includingmagnetic and electrostatic analysers, an auxiliary electrostaticanalyser, and two ion collectors, comprising the steps of:

a. introducing a substance into said ion source means and forming twoion beams therefrom;

b. passing the two ion beams through the common analyser means;

c. thereafter collecting one of said ion beams directly on one of saidion collectors; and,

d. passing the other of said ion beams through said auxiliaryelectrostatic analyser, performing an auxiliary electrostatic analysison said other ion beam and subsequently collecting ions passing throughsaid auxiliary electrostatic analyser on the other of said ioncollectors.

7. The method of claim 6 wherein the auxiliary electrostatic analysis isperformed by a fixed electric field within said auxiliary electrostaticanalyzer.

8. The method of claim 6 wherein the auxiliary electrostatic analysis isperformed by making a scanning variation of an electric field withinsaid auxiliary electrostatic analyzer.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION h 1.2 1974 PatentNo. 3 796 872 Dated Marc I Inventor(s) Thomas Ollver Merren It iscertified that error appears in the shove -identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 6', line 15, delete "6" and substitute (SEAL) Attest:

McCOY M. GIBSON, JR. Attesting Officer C. MARSHALL DANN Commissioner ofPatents FORM PO-105OH0-69)

1. A method of mass spectrometry performed with a plural beam massspectrometer wherein a plurality of ion beams formed from a commonsubstance are passed through a common analyser means including magneticand electrostatic analysers and collected by individual ion collectors,comprising the steps of further electrostatically analysing one of thebeams between the common analyser means and the respective ioncollector, and directly collecting at least one other ion beam on arespective other ion collector without electrostatic analysis of saidother ion beam between the common analyser means and said other ioncollector.
 2. The method of claim 1, wherein metastable ions arecollected by said respective ion collector and parent ions of saidmetastable ions are collected by said other ion collector.
 3. The methodof claim 1, wherein parent ions are collected by said respective ioncollector and metastable ions are collected by said other ion collector.4. The method of claim 1 wherein the further electrostatic analysis ofsaid one of the beams is performed by making a scanning variation of anelectrostatic field.
 5. The method of claim 1 wherein the furtherelectrostatic analysis of said one of the beams is performed with afixed electric field.
 6. A method of mass spectrometry performed with adouble-beam mass spectrometer having ion source means, a common analysermeans including magnetic and electrostatic analysers, an auxiliaryelectrostatic analyser, and two ion collectors, comprising the steps of:a. introducing a substance into said ion source means and forming twoion beams therefrom; b. passing the two ion beams through the commonanalyser means; c. thereafter collecting one of said ion beams directlyon one of said ion collectors; aNd, d. passing the other of said ionbeams through said auxiliary electrostatic analyser, performing anauxiliary electrostatic analysis on said other ion beam and subsequentlycollecting ions passing through said auxiliary electrostatic analyser onthe other of said ion collectors.
 7. The method of claim 6 wherein theauxiliary electrostatic analysis is performed by a fixed electric fieldwithin said auxiliary electrostatic analyzer.
 8. The method of claim 6wherein the auxiliary electrostatic analysis is performed by making ascanning variation of an electric field within said auxiliaryelectrostatic analyzer.